Neuromuscular blockers: interaction with aminoglycosides: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Neuromuscular blockers: interaction with aminoglycosides

Sample item

A 55-year-old man undergoing bowel surgery receives vecuronium. Intraperitoneal gentamicin lavage is used at the end, and he remains weak and poorly ventilated, with fade on train-of-four stimulation although neostigmine has been given. Which mechanism best explains the prolonged block?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Aminoglycosides reduce presynaptic acetylcholine release and postjunctional sensitivity, adding to the block

Aminoglycosides interfere with calcium-dependent acetylcholine release and decrease the sensitivity of the motor endplate, so they potentiate non-depolarising blockers and can resist reversal. Magnesium, volatile anaesthetics and calcium channel blockers have similar additive effects. Management is supportive ventilation with calcium and further reversal, such as sugammadex for aminosteroid blockers.

Option by option

  • A. Gentamicin inhibits plasma cholinesterase and so delays vecuronium breakdown

    Vecuronium is eliminated by the liver and kidney, not by plasma cholinesterase, which gentamicin does not inhibit.

  • B. Aminoglycosides reduce presynaptic acetylcholine release and postjunctional sensitivity, adding to the block (correct)

    Reduced presynaptic release and postjunctional sensitivity add to competitive blockade at the endplate.

  • C. Gentamicin induces hepatic enzymes that convert vecuronium to an active metabolite

    Vecuronium is not converted to a more active metabolite through enzyme induction by gentamicin.

  • D. Gentamicin displaces vecuronium from plasma proteins

    Protein-binding displacement does not explain a persistent block of this kind and gentamicin is not a binding competitor.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Aminoglycosides reduce presynaptic acetylcholine release and postjunctional sensitivity, adding to the block. Aminoglycosides interfere with calcium-dependent acetylcholine release and decrease the sensitivity of the motor endplate, so they potentiate non-depolarising blockers and can resist reversal.

Why is "Gentamicin inhibits plasma cholinesterase and so delays vecuronium br…" not the answer?

Vecuronium is eliminated by the liver and kidney, not by plasma cholinesterase, which gentamicin does not inhibit.

Why is "Gentamicin induces hepatic enzymes that convert vecuronium to an acti…" not the answer?

Vecuronium is not converted to a more active metabolite through enzyme induction by gentamicin.

Why is "Gentamicin displaces vecuronium from plasma proteins" not the answer?

Protein-binding displacement does not explain a persistent block of this kind and gentamicin is not a binding competitor.

What concept does this question test?

It tests Neuromuscular blockers: interaction with aminoglycosides in Pharmacology. Magnesium, volatile anaesthetics and calcium channel blockers have similar additive effects. Management is supportive ventilation with calcium and further reversal, such as sugammadex for aminosteroid blockers.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Neuromuscular blockers: interaction with aminoglycosides?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.